Dielectric material



July 28, 1931. s. BQYER DIELECTRIC MATERIAL Filed March 16, 1927 2 Sheets-Sheet 2 H/Ww O I H FB r. p r o ne m a. A e .5 UJ 5 nd 1D Patented July 28, 1931 UNITED STATES PATENT OFFICE SYLVESTER BOYER, OF LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK DIELECTRIC MATERIAL Application filed March 16, 1927. Serial No. 175,868.

My invention relates to dielectric material and in particular it relates to dielectric material which is especially adapted for use in connection with electric condensers and the like.

In my co-pending application, Serial No. 73,273, filed December 4, 1925, now Patent No. 1,769,874 granted July 1, 1930, I have pointed out that material such as mono-nitrobenzene and nitro-toluene are especially adapted for use as a dielectric in connection with condensers and the like when highly purified, as these have high specific inductive capacity, and when purified have high specific resistivity and high dielectric strength. Condensers, however, are very often subjected to quite low temperatures and the freezing point of nitro-benzene is somewhere around 4.6 deg. C. I have found that it is undesirable to allow condensers to freeze for the reason that it causes a variation in the specific inductive capacity or permittivity of the condenser dielectric and it also causes a substantial variation in the power factor of the condenser. These variations are undesirable for-the reason that they are sometimes responsible for the overheating or breaking down of the condenser. I have found it is necessary sometimes to lower the freezing point of such dielectric materials as nitro-benzene by the addition of some other dielectric material such as nitro-toluene, the

freezing point of which latter is about 10 deg. below zero C.

By mixing nitro-benzene with nitro-toluene I obtain a dielectric product having substantially the same characteristics as nitrobenzene but having a much lower freezing point. For example, the product has high specific resistivity, that is, of the order of 10 ohms per centimeter cube and over, high dielectric strength comparable with that of transil oil and high specific inductive capacity of the order of 10 and over. The results obtained by mixing nitro-benzene with nitrotoluene are shown in Fig. 1. Instead of nitro-toluene other liquids may be substituted, for example, di-nitro-benzene and mono-chloro-benzene, and the results are indicated in Figs. 2 and 3. I

In Fig. 4 I have shown a condenser of the usual type inits container saturated with the material of the invention, while in Fig. 5 I have shown the condenser removed from the container.

In determining the maximum percentage of material to be added to the nitro-benzene, care must be exercised in the selection of the ingredient to be added inasmuch as after a certain maximum percentage of the ingredient is added any further addition in percentage will cause the freezing point to rise, as indicated in Fig. 3. Technically this turning point is known as the eutectic point. The curve in Fig. 3 is for a mixture of nitro-ben- .zenes, namely mono-nitro-benzene and dinitro-benzene.

What has been said with. respect to the freezing point of nitro-benzen e applies to the boiling point. In other words, by adding nitro-toluene to nitro-benzene the boiling point of'the mixture is raised to a point above that of nitro-benzene. Consequently I find that by adding, for example, nitrotoluene to nitro-benzene I can increase the liquid range of the material from freezing point to boiling point. Therefore, if it is found that the boiling point of nitro-benzene is too low for a specific use, as for example for use in connection with a particular form of condenser, or in a cable or the like, this point can be readily raised by the addition of an ingredient such as nitrotoluene, dinitro-benzene and the like. Nitro-toluene has a boiling point of about 222 degrees C. while nitro-benzene has a boiling point of about 212 degrees C. The result is that by mixing the two the boiling point of the mixture is raised above that of the nitro-benzene. Similar results follow by the addition of the other ingredients mentioned.

Ordinarily nitro-benzene has low resistivity and ordinarily nitro-toluene has low resistivity. But both of these materials have a high specific inductive capacity of the O1"- der of from 18 to 34. The low resistivity is due to the presence of impurities in either of these materials which; impurities may be in the form of water, dissociated acids or salts of such acids, or even the acids in their natural state or the acids in an undissociated state. I find that these impurities may be removed by mixing aluminum oxide with either of the ingredients and heating to a temperature of about to degrees C. and distilling. Therefore, these materials may be conditioned or purified so as to have a specific resistivity of the order of 1 x 10 ohms per centimeter cube and also a high dielectric strength. In mixing these liquids, as above indicated, to lower the freezing point, I find that these characteristics of the ingredients are still preserved.

One form of condenser in which the dielectric of the invention may be used is shown in Fig. 5. This condenser is provided with terminals a and b which are connected with the plates of the condenser within the container 0 through the bushings e and f by means of leads 9 and it. As shown the lead 9 is connected with a number of metal strips 71 which connect with the metal elements of the condenser in the usual manner. The lead h is connected to another set of similar strips which are covered by an insulating plate j which latter prevents any short-circuiting between such terminals and the frame. The protecting plate for the terminal 11 is not shown for clearness of illustration. The form of condenser shown in Fig. 4: is made in four sections all of which are clamped together by means of clamping plates is. After the sections are clamped together as indicated, they are placed within the container 0 which container is filled with nitro-benzene of the invention. It will be understood that the condenser is vacuum treated and impregnated with nitro-benzene, the method being the same as that used in the manufacture of condensers immersed in oil.

It will be understood that Whereas I have described my invention by citing specific materials and specific proportions, I do not wish to be so limited inasmuch as the materials may be varied and the proportions may be varied without departing from the spirit and scope of the invention as described and claimed herein.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A dielectric mixture consisting of nitro-benzene and nitro-toluene.

2. A dielectric mixture consisting of two liquids and having a resistivity of the order of 10 ohms per centimeter cube and high specific inductive capacity of the order of 10.

In witness whereof, I have hereunto set my hand this twelfth day of March, 1927. SYLVESTER BOYER'. 

